Switch-Mode Converter Operating in a Hybrid Discontinuous Conduction Mode (DCM)/Continuous Conduction Mode (CCM) That Uses Double or More Pulses in a Switching Period

ABSTRACT

A switching converter controller and method for controlling a switch-mode converter in a hybrid discontinuous conduction mode (DCM)/continuous conduction mode (CCM) mode are disclosed. The hybrid mode involves using double (two) or more switching pulses in a switching period of a control signal for controlling the switch-mode converter. The switching period is defined by a switch on-time duration, a switch off-time duration, and an N number of switching pulses. N is an integer greater than one. An inductor current through the inductor of the switch-mode converter is zero before an initial switching pulse, is zero after a last switching pulse, and is non-zero for all other times within the switching period. The switch-mode-converter controller can be used as a power factor correction controller for a power factor corrector. The switch-mode converter controller can be implemented on a single integrated circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) and 37 C.F.R§1.78 of U.S. Provisional Application No. 60/915,547, filed May 2, 2007,and entitled “Power Factor Correction (PFC) Controller Apparatuses andMethods,” and is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the field of signalprocessing, and, more specifically, to a switch-mode converter operatingin a hybrid discontinuous conduction mode (DCM)/continuous conductionmode (CCM).

2. Description of the Related Art

Switch-mode converters are Direct Current (DC) to Direct Current (DC)converters that convert from one DC voltage level to another DC voltagelevel. A switch-mode converter operates by temporarily storing inputenergy at one voltage level and respectively releasing the energy at itsoutput at a different voltage level. Two main exemplary switch-modeconverters are a switch-mode boost converter and a switch-mode buckconverter. Both of these switch-mode converters are well known in theart.

An exemplary switch-mode boost converter/stage 102 is shown in a typicalexemplary power factor corrector 100 in FIG. 1. Power factor correctorsoften utilize a switch-mode boost stage to convert alternating current(AC) voltages (such as line/mains voltages) to direct current (DC)voltages or DC-to-DC wherein the input current is proportional to theinput voltage. Power factor correctors provide power factor corrected(PFC) and regulated output voltages to many devices that utilize aregulated output voltage. Switch-mode boost converter/stage 102 will nowbe explained, in more detail in the context of power factor corrector100.

Voltage source 101 supplies an alternating current (AC) input voltageV_(in)(t) to a full-wave diode bridge rectifier 103. The voltage source101 (e.g., voltage V_(in)(t)) is, for example, a public utility, such asa 60 Hz/120 V line (mains) voltage in the United States of America or a50 Hz/230 V line (mains) voltage in Europe. The input rate associatedwith input voltage V_(in)(t) is the frequency of voltage source 101(e.g., 60 Hz in the U.S. and 50 Hz in Europe). The rectifier 103rectifies the input voltage V_(in)(t) and supplies a rectified,time-varying, line input voltage V_(x)(t) to the switch-mode boost stage102. The actual voltage at any time t is referred to as theinstantaneous input voltage. Unless otherwise stated, the term “linerate” is hereafter referred to and defined as the rectified inputfrequency associated with the rectified line voltage V_(x)(t). The linerate is also equal to twice the input frequency associated with inputvoltage V_(in)(t). The rectified line input voltage is measured andprovided in terms of Root Mean Square (RMS) voltage, e.g., V_(rms).

The switch-mode boost converter/stage 102 includes a switch 108 (e.g.,Field Effect Transistor (FED) by which it is controlled and providespower factor correction (PFC) in accordance with how switch 108 iscontrolled. The switch-mode boost converter/stage 102 is also controlledby switch 108 and regulates the transfer of energy from the rectifiedline input voltage V_(x)(t) through inductor 110 to capacitor 106 via adiode 111. The inductor current i_(L) ramps ‘up’ when the switch 108conducts, i.e. is “ON”. The inductor current i_(L) ramps down whenswitch 108 is nonconductive, i.e. is “OFF”, and supplies current i_(L)to recharge capacitor 106. The time period during which inductor currenti_(L) ramps down is commonly referred to as the “inductor flyback time”.

A switch-mode converter controller 114, such as an exemplary powerfactor correction (PFC) controller, controls switch 108. Switch-modeconverter controller 114 controls switch 108 and, thus, controls powerfactor correction and regulates output power of the switch-mode boostconverter/stage 102. The goal of power factor correction technology isto make the switch-mode boost converter/stage 102 appear resistive tothe voltage source 101. Thus, the switch-mode converter controller 114attempts to control the inductor current i_(L) so that the averageinductor current i_(L) is linearly and directly related to the rectifiedline input voltage V_(x)(t). Unitrode Products Datasheet entitled“UCC2817, UCC2818, UCC3817, UCC3818 BiCMOS Power Factor Preregulator”(SLUS3951) dated February 2000—Revised February 2006 by TexasInstruments Incorporated, Copyright 2006-2007 (referred to herein as“Unitrode datasheet”) and International Rectifier Datasheet entitled“Datasheet No PD60230 rev C IR1150(S(PbF) and IR 1150I(S)(PbF)” datedFeb. 5, 2007 by International Rectifier, describe examples of a FTCcontroller. The PPC controller Supplies a pulse width modulated (PWM)control signal CS₀ to control the conductivity of switch 108.

Two modes of switching stage operation exist: Discontinuous ConductionMode (“DCM”) and Continuous Conduction Mode (“CCM”). In DCM, switch 108of switch-mode converter controller 114 (or boost converter) is turnedon (e.g., “ON”) when the inductor current equals zero. In CCM, switch108 of switch-mode converter controller 114 (or boost converter)switches “ON” when the inductor current is non-zero, and the current inthe energy transfer inductor 110 never reaches zero during the Switchingcycle. In CCM, the current swing is less than in DCM, which results inlower I²R power losses and lower ripple current for inductor currenti_(L) which results in lower inductor core losses. The lower voltageswing also reduces Electro Magnetic Interference (EMI), and a smallerinput filter can then be used. Since switch 108 is turned “OFF” when theinductor current i_(L) is not equal to zero, diode 111 needs to be veryfast in terms of reverse recovery in order to minimize losses.

The switching rate for switch 108 is typically operated in the range of20 kHz to 100 kHz. Slower switching frequencies are avoided in order toavoid the human audio frequency range as well as avoid increasing thesize of inductor 110. Faster switching frequencies are typically,avoided since they increase the switching losses and are more difficultto use in terms of meeting Radio Frequency Interference (RFI) standards.

Capacitor 106 supplies stored energy to load 112. The capacitor 106 issufficiently large so as to maintain a substantially constant linkoutput voltage V_(c)(t) through the cycle of the line rate. The linkoutput voltage V_(c)(t) remains substantially constant during constantload conditions. However, as load conditions change, the link outputvoltage V_(c)(t) changes. The switch-mode converter controller 114responds to the changes in link output voltage V_(c)(t) and adjusts thecontrol signal CS₀ to resume a substantially constant output voltage asquickly as possible. The switch-mode converter controller 114 includes asmall capacitor 115 to prevent any high frequency switching signals fromthe line (mains) input voltage V_(in)(t).

Switch-mode converter controller 114 receives two feedback signals, therectified line input voltage V_(x)(t) and the link output voltageV_(c)(t), via a wide bandwidth current loop 116 and a slower voltageloop 118. The rectified line input voltage V_(X)(t) is sensed from node120 between the diode rectifier 103 and inductor 110. The link outputvoltage V_(c)(L) is sensed from node 122 between diode 111 and load 112.The current loop 116 operates at a frequency f_(c) that is sufficient toallow the switch-mode converter controller 114 to respond to changes inthe rectified line input voltage V_(X)(t) and cause the inductor currenti_(L) to track the rectified line input voltage V_(x)(t) to providepower factor correction. The inductor current i_(L) controlled by thecurrent loop 116 has a control bandwidth of 5 kHz to 10 kHz. The voltageloop 118 operates at a much slower frequency control bandwidth of about5 Hz to 20 Hz. By operating at 5 Hz to 20 Hz, the voltage loop 118functions as a low pass filter to filter a harmonic ripple component ofthe link output voltage V_(c)(t).

FIG. 1B shows an exemplary switch-mode buck converter 150 that comprisesthe similar elements that were used for switch-mode boostconverter/stage 102 in FIG. 1A. Switch-mode converter controller 114 iscoupled to switch-mode buck converter 150. Switch-mode convertercontroller 114 executes a switch control algorithm which definesswitching characteristics for the switch control Signal CS₀ that is usedto control switch 108.

Switch-mode buck converter 150 includes switch 108 coupled in serieswith inductor 110. One end of diode 111 is coupled between switch 108and inductor 110 at the positive side of the input voltage Vin. Theother end of diode 111 is coupled to the negative side of input voltageVin. Capacitor 106 is coupled across the output voltage Vout. Incontrast, for a switch-mode buck converter (e.g., switch-mode buckconverter 150), the average inductor current is the output current ofthe buck converter, and the input current is approximately calculatedas:

Iin=Iout*Vout/Vin  Equation A

This mode of operation for the switch-mode buck converter requires theoutput voltage Vout to be less than the input voltage Vin. In someapplications, the output current Iout is directly controlled, such asfor LED lighting. In other applications, the output voltage Voutrequires regulation, and current control is still desirable. In FIG. 1B,switch-mode converter controller 114 is coupled to switch mode buckconverter 150 in the manner shown. The current loop 152 operates at afrequency f_(c) that is sufficient to allow the switch-mode convertercontroller 114 to respond to changes in the rectified line input voltageV_(x)(t). A voltage feedback loop 154 controls the input to a currentregulator.

With reference now to FIG. 2A, a plot 200 of exemplary DCM currentwaveforms is shown for a switch control algorithm for controlling aswitch (e.g., switch 108) of a switch-mode boost converter (e.g.,switch-mode boost converter/stage 102) at a time scale of 10microseconds wherein the target current i_(target) in FIG. 2A is set at0.8 Amp. Plot 200 shows the current waveform for inductor current i_(L)through inductor 110. Exemplary on-time t_(on) and off-time t_(off) arealso shown. In this case, since the target current i_(target) is low andbelow the exemplary minimum target current i_(target) of 1 Amp foroperating in CCM, the switch-mode boost converter/stage 102 operates inDCM.

With reference now to FIG. 2B, a plot 202 of exemplary DCM currentwaveforms is shown for a switch control algorithm for controlling aswitch (e.g., switch 108) of a switch-mode boost converter (e.g.,switch-mode boost converter/stage 102) at a time scale of 10microseconds wherein the target current i_(target) in FIG. 2A is set ator very close to 1 Amp (e.g., the exemplary minimum target current leveli_(target)). Plot 202, shows the current waveform for inductor currenti_(L) through inductor 110. Exemplary on-time t_(on) and off-timet_(off) are again shown. In this case, since the target currenti_(target) is at or very close to the minimum target current i_(target)of 1 Amp for operating in DCM, the switch-mode boost converter/stage 102is in a transitional conduction mode in which operation of theswitch-mode boost, stage/converter 102 may be able to be switched toCCM.

Several advantages of operating the switch-mode converter (e.g.,switch-mode boost converter 102) in CCM exist. For example,“shoot-through” conduction, in which the diode (e.g., diode 111) and theswitch (e.g., switch 108) are both on for the same (transient) time,does not exist. The switch (e.g., switch 108) always turns on with zerocurrent (other than for parasitics). These advantages allow for goodswitch-mode conversion efficiency at low cost. Also, the control of theswitch for the switch-mode converter can be entirely open loop, with noneed to sense the actual inductor current.

However, there are disadvantages for operating a switch-mode converterin CCM. One disadvantage is that high ripple in the inductor current(e.g., inductor current i_(L)) exists. The switch-mode converter in CCMalso has a limited power range. In CCM, the switch-mode converter has apeak current that is limited by the saturation limit of the inductor.The switch-mode converter in CCM is also limited by the currentcapability of the switch (e.g., switch 108) and diode (e.g., diode 111).

In various instances, transient power produced from a system utilizing aswitch-mode converter is higher than the rated maximum. In a pure DCMsystem, components must be rated for the peak transient. Thus, it may bedesired to allow a system with a switch-mode converter operating in DCMto enter into CCM operation on a temporary basis to allow the system todeliver more power. However, controlling such a system in CCM withoutcurrent sensing has made for unreliable designs, as the inductor currentcan easily “run away” and become excessive.

Thus, it is needed and desired to provide a switch-mode converter thatcan operate in a mode that has the advantages of both DCM and CCM andthat minimizes or eliminates at least some of the disadvantages ofoperating in CCM and/or DCM. It is further needed and desired to providea way to operate the switch-mode-converter in a hybrid DCM/CCM mode andto be able to operate in such a mode such that current sensing is notrequired. It is additionally needed and desired to be able to operatesuch a switch-mode converter in a hybrid DCM/CCM that can be used in aPFC system as well as for a number of other applications.

SUMMARY OF THE INVENTION

A switching converter controller and method that use a finite statemachine configured to operate and control a switch-mode converter in ahybrid discontinuous conduction mode (DCM)/continuous conduction mode(CCM) mode are disclosed. The switch-mode converter has a switch and aninductor coupled to the switch, and the switch-mode converter receivesan input voltage and provides an output voltage. The hybrid modeinvolves using double (two) or more switching pulses in a switchingperiod of a control signal for controlling the switch-mode converter.The switching period is defined by a switch on-time duration, a switchoff-time duration, and an N number of switching pulses. N is an integergreater than one. An inductor current through the inductor of theswitch-mode converter is zero before an initial switching pulse, is zeroafter a last switching pulse, and is non-zero for all other times withinthe switching period.

In one exemplary embodiment, the N number of switching pulses is setequal two, and the switch-mode converter controller operates theswitch-mode converter in a hybrid DCM/CCM double-pulse mode. In anotherexemplary embodiment, the N number of switching pulses is set equalthree, and the switch-mode converter controller operates the switch-modeconverter in a hybrid DCM/CCM triple-pulse mode.

In a further exemplary embodiment, for a subsequent switching pulse thatis after the initial switching pulse and before the last switchingpulse, the switch is turned on for a fraction of the on-time durationand the switch is turned off for the fraction of the off-time duration.The fraction is set to a value that is greater than zero and less thanone and is defined by a ratio of a width of the subsequent switchingpulse to a width of the initial switching pulse. The fraction can beselected as an exemplary optimal value in a range between 0.25 and 0.50.

Furthermore, the switching converter controller can be used as a powerfactor correction (PFC) controller for controlling is a switch-modeboost converter of a power factor corrector. Also, the switch-modeconverter controller can be implemented on a single integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features and advantages made apparent to those skilled in theart by referencing the accompanying-drawings. The use of the samereference number throughout the several figures designates a like orsimilar element.

FIG. 1A depicts an exemplary switch-mode boost converter/stage coupledto a switch-mode converter controller that is power factor correction(PFC) controller wherein the switch-mode boost converter/stage is beingused in a power factor corrector.

FIG. 1B depicts an exemplary switch-mode buck converter/stage coupled toa switch-mode converter controller.

FIG. 2A depicts exemplary current waveforms for a switch controlalgorithm wherein the exemplary target current is set below a minimumtarget current for operating in CCM (at 0.8 Amp) and the switch-modeconverter operates in DCM.

FIG. 2B depicts exemplary current waveforms for a switch controlalgorithm wherein the exemplary target current is set at or close to aminimum target current for operating in CCM (at 1 Amp) and theswitch-mode converter still operates in DCM but may be able or close toswitching to alternatively operating in CCM.

FIG. 3A depicts an exemplary switching period of current waveforms for aswitch control algorithm wherein the exemplary target current is set ator close to a minimum target current for operating in CCM (at 1 Amp) andthe switch-mode converter still operates in DCM and FIG. 3A is forcomparing with FIG. 3B.

FIG. 3B depicts an exemplary switching period of current waveforms for aswitch control algorithm wherein the switch-mode converter operates inthe hybrid. DCM/CCM double-pulse mode.

FIG. 4 depicts a state diagram for implementing by the switch-modeconverter controller shown in FIGS. 1A and 1B the preferred switchcontrol algorithm as characterized by the exemplary current waveforms ofFIG. 3B for operating the switch-mode converter in the hybrid DCM/CCMdouble-pulse mode.

FIG. 5A depicts an exemplary switching period of current waveforms for aswitch control algorithm, wherein the exemplary target current is set ator close to a minimum target current for operating in CCM (at 1 Amp) andthe switch-mode converter still operates in DCM and FIG. 5A is forcomparing with FIG. 5B.

FIG. 5B depicts an exemplary switching period of current waveforms for aswitch control algorithm wherein the switch-mode converter operates inthe hybrid DCM/CCM triple-pulse mode.

FIG. 6 depicts a state diagram for implementing by the switch-modeconverter controller shown in FIGS. 1A and 1B the preferred switchcontrol algorithm as characterized by the exemplary current waveforms ofFIG. 5B for operating the switch-mode converter in the hybrid DCM/CCMtriple-pulse mode.

FIG. 7 depicts an exemplary power factor corrector that includes aswitch-mode converter controller (PFC controller) on a single integratedcircuit, that is able to incorporate and implement the FSM algorithms ofthe present invention, wherein the switch-mode converter controller iscoupled to a switch-mode converter.

DETAILED DESCRIPTION

The present invention provides a switch-mode converter that operates ina mode, which is defined and disclosed as a hybrid. DCM/CCM mode. Aswitch-mode converter operating in the hybrid DCM/CCM mode hasadvantages of both DCM and CCM. The hybrid DCM/CCM mode also minimizesor eliminates at least some Of the disadvantages of operating in CCMand/or DCM. For example, a switch-mode converter operating in the hybridDCM/CCM mode does not require the use of current sensing. Significantlymore current can be delivered by the hybrid DCM/CCM mode as contrastedwith the DCM, given the same power components. Two exemplary embodimentsfor operating the switch-mode converter will be discussed in detail inthis specification: a hybrid DCM/CCM double-pulse mode and a hybridDCM/CCM triple-pulse mode. However, the present invention is not in anyway limited, to being implemented by the use of just a double-pulse ortriple pulse defined in the switching period, and additional pulses inthe switching period may further be added and utilized as well.Practically, the number of pulses implemented in the switching periodmay be limited by the eventual mismatch between the current in the idealmodel and the actual circuit that exists as additional pulses are addedand used. Furthermore, such a switch-mode converter operating in ahybrid DCM/CCM can be used in a PFC system as well as for a number ofother systems and applications. The systems and applications whichincorporate the present invention are not in any way limited to the onesdisclosed in this specification.

Switch-mode converter controller 114 of FIGS. 1A and 1B can be utilizedand configured to operate the respective switch-mode converter 100 or150 in the hybrid DCM/CCM mode in accordance with the principles of thepresent invention. Switch-mode converter 114 further has a finite statemachine (FSM) 117 which includes a timer. The switch control algorithmsdefined by the characteristics of the exemplary current waveforms inFIGS. 3B and 5B and the corresponding state diagrams in FIGS. 4 and 6,which will be discussed in more detail later, can be implemented as FSMalgorithms that are executed by FSM 117 and the timer. Thus, elementsand components of switch-mode controller 114 and switch-mode converter100 or 150 will be referenced when discussing the present invention inthis specification.

FIG. 3A depicts a plot 300 which shows an exemplary switching period ofcurrent waveforms for a switch control algorithm. The switch controlalgorithm would be used, for example, to control switch 108 ofswitch-mode converter 102 or 150. In the exemplary current waveforms ofFIG. 3A, the target current is set at or close to the exemplary minimumtarget current for operating a switch-mode converter in CCM, that is, 1Amp in this example. Plot 300 shows that the exemplary switching periodrepresented by the total time period TT. The total time period TT is thesum of the on-time duration T₁ and off-time duration T₂ of switch 108,that is,

TT=T ₁ +T ₂  Equation B

Referring specifically to the example in plot 300, on-time duration T₁is equal to 4 microseconds while off-time duration T₂ is equal to 2microseconds. Thus, the total time period TT for the switching period is6 microseconds. The ratio of the on-time duration T₁ to the off-timeduration T₂ is determined by the input and output voltages. Inimplementing a switch control algorithm based on the characteristics inplot 300 of FIG. 3A, the switch-mode converter 102 or 150 still operatesin DCM. However, the switch-mode converter 102 or 150 may be able orclose to switching to alternatively to operate in CCM since the targetcurrent is at the exemplary minimum target current level of 1 Amp foroperating in CCM. Plot 300 of FIG. 3A will be used for comparisonpurposes with plot 302 of FIG. 3B.

FIG. 3B shows a plot 302 which depicts an exemplary switching period ofcurrent waveforms for a switch control algorithm in accordance with theprinciples of the present invention. The switch control algorithm wouldbe used, for example, to control switch 108 of switch-mode converter 102or 150. In the exemplary current waveforms of FIG. 3B, the switch-modeconverter 102 or 150 operates in the hybrid DCM/CCM double-pulse mode.

Generally, the hybrid DCM/CCM mode for a switch mode converter involvesadding one or more additional pulses (i.e., adding n pulses) to theswitching period to further increase the average current i_(average) ofthe inductor current i_(L). For example, the hybrid DCM/CCM double-pulsemode involves having two switching pulses P1 and P2 defined in theswitching period as shown in plot 302. Switching pulse P2 is defined andused in addition to the switching pulse P1 in the switching period. Asanother example, the hybrid DCM/CCM triple-pulse mode involves havingthree switching pulses P1, P2, and P3 defined in the switching period asshown in plot 502. Switching pulses P2 and P3 are defined and used inaddition to the switching pulse P1 in the switching period.

The number of n pulses added is limited by the inaccuracy of the currentmodel. Such inaccuracies include mismatches generally caused byparasitic components and non-zero on-voltages. For high voltage systems(e.g., 400 Volts), three to four pulses can be added to the switchingperiod without the occurrence of significant current control error.Thus, these circuit non-idealities drive the average current i_(average)for inductor current i_(L) lower than what is modeled by simplemathematics so that destructive operation of the circuit is avoided. Themodel currents will drift, away from the actual currents until such timeas the inductor current i_(L) is allowed to go to zero, and the processis re-started. The drift limits the practical number of pulses that canbe added to the switching period. The number of subsequently addedpulses, and hence additional current capacity, can be increased withmore accurate modeling.

The general mathematical relationships for adding pulses (e.g., adding npulses) in the switching period for controlling a switch in theswitch-mode converter so that the switch-mode converter can operate inthe hybrid DCM/CCM mode are now discussed. If n number of pulses areadded to the switching period; the total charge transferred is definedas:

Total Charge Q=Q1*(1+n(1−(1−r ²))  Equation C

where Q1 is the total charge for a single period of the inductor currenti_(L) operating in DCM (and not in the hybrid DCM/CCM mode) operating atthe same peak current; n is the number of added pulses; and r is afraction defined by the ratio of the width of subsequent pulses to thewidth of the initial pulse. The optimum value selected for r is usuallyin the range of 0.25 and 0.50.

Since n number of pulses is added to the switching period, the totaltime duration TT′ (e.g., in FIGS. 3B and 5B) of the switching periodbecomes respectively longer than the total timer duration TT (e.g., inFIGS. 3A and 5B). For example, a first off-time duration r*T₂ is addedto the total switching period, and a second on-time duration r*T₁ isalso added to the total switching period. Thus, the total time durationTT′ for the switching period is then determined by:

TT′=(T ₁ +T ₂)*(1+n*r)  Equation D

In other words, the total time duration TT′ for the switch-modeconverter operating in the hybrid DCM/CCM mode is defined as (1+n*r)longer than the switching time period TT=(T₁+T₂), that is, the totalswitching time period defined for when the switch-mode converter simplyoperates in DCM.

The average current for operating the switch-mode converter in thehybrid DCM/CCM mode is defined as follows:

i _(average) =Q/TT′=(Q1*(1+n(1−(1−r)²)))/(T ₁ +T ₂)*(1+n*r)  Equation E

However, the average current (e.g., target current i_(target)) when theswitch-mode converter is operating in DCM is defined as follows:

i _(target) =Q1/(T ₁ +T ₂)=Q ₁ /TT  Equation F

Thus, operating the switch-mode converter in the hybrid DCM/CCM modeprovides an improved/additional average current over and in comparisonwith operating the switch-mode converter simply in the DCM mode, definedby the following ratio:

i _(average) /i _(target)=(1+n(1−(1−r ²))/(1+n*r)  Equation G

In other words, operating the switch-mode converter in the hybridDCM/CCM mode provides i_(average)/i_(target) more times average currentthan operating the switch-mode converter simply in DCM. r is selectedwithin the range of 0.25 to 0.50 based on an optimal value calculation.Such a calculation is achieved by performing a derivative on the ratioi_(average)/i_(target) defined in Equation G.

Referring now to the specific example in plot 302 of FIG. 3B, the chargearea Q1 defined by a first set of bolded boundaries represents thecharge defined in a first portion of the current waveform for inductorcurrent i_(L) when the switch-mode converter is operating in the hybridDCM/CCM mode. The area Q1 in FIG. 3B is identical to the area Q1 definedby the bolded boundaries in FIG. 3A since Q1 represents the chargedefined for a single switching period of the current waveform forinductor current i_(L) when the switch-mode converter is simplyoperating in DCM. Plot 302 further shows an additional charge area Q2defined by a second set of bold boundaries. Area Q2 defines new/addedcharge for a second portion of the current waveform for inductor currenti_(L) when the switch-mode converter is operating in the hybrid DCM/CCMmode. Since two pulses. P1 and P2 (e.g., total N number of pulses=2pulses in this case wherein N>1) are defined in the switching period,the switch-mode converter in this case is considered to be operating inthe hybrid DCM/CCM double-pulse mode.

In this example of FIG. 3B, n is equal to 1 since pulse P2 is added, andr is set equal to 0.5. The total charge being transferred for theswitching period is then calculated as:

Total Charge Q=Q1*(1+1(1−(1−0.5)²))=1.75*Q1  Equation H

The total time duration TT for the switching period is defined as:

$\begin{matrix}\begin{matrix}{{TT}^{\prime} = {\left( {T_{1} + T_{2}} \right)*\left( {1 + {1*0.5}} \right)}} \\{= {{1.5*\left( {T_{1} + T_{2}} \right)} =}} \\{= {1.5*{TT}}} \\{= {1.5\left( {4\mspace{14mu} {{microsec}.{+ 2}}\mspace{14mu} {{microsec}.}} \right)}} \\{= {9\mspace{14mu} {{microseconds}.}}}\end{matrix} & {{Equation}\mspace{14mu} I}\end{matrix}$

In other words, the total time duration TT′ for the switching perioddefined when the switch-mode converter is operating in the hybridDCM/CCM mode (e.g., FIG. 3B) is 1.5 times longer than the switchingperiod defined when the switch-mode converter is simply operating in DCM(e.g., FIG. 3A). FIG. 3B also shows that the total time duration TT′ isthe sum of on-time duration T₁+off-time duration T₂/2+on-time durationT₁/2+off-time duration T₂. This break down of the total time durationTT′ will be used for the timing in controlling activation anddeactivation of the switch (e.g., switch 108).

The current comparison ratio between the hybrid DCM/CCM mode and the DCMmode is then calculated as follows:

$\begin{matrix}\begin{matrix}{\frac{i_{average}}{i_{target}} = \frac{\left( {1 + {1\left( {1 - \left( {1 - 0.5} \right)^{2}} \right)}} \right)}{\left( {1 + {1*0.5}} \right)}} \\{= \frac{1.75}{1.5}} \\{= 1.1666}\end{matrix} & {{Equation}\mspace{14mu} J}\end{matrix}$

That is, the average current provided when the switch-mode converter isoperating in the hybrid DCM/CCM double-pulse mode is 1.1666 times theaverage current when the same switch-mode converter is simply operatingin DCM. This comparison is shown in FIG. 3B where the i_(average) lineis at 1.1666 Amp while the i_(target) line is at 1 Amp.

With reference now to FIG. 4, a state diagram 400 is shown for the FSM117 in FIGS. 1A and 1B. State diagram 400 shows how the FSM algorithmimplements the preferred switch control algorithm as characterized bythe exemplary current waveforms of FIG. 3B for operating the switch-modeconverter in the hybrid DCM/CCM double-pulse mode. The timer that is inFSM 117 is used in implementing and executing the switch timing for theFSM algorithm (e.g., Switch control algorithm).

State diagram 400 shows that for this preferred control techniqueembodiment, FSM algorithm moves to a state S0 in which the timer isreset. At state S0, switch 108 is on, and the timer waits for an on-timeduration T₁ (e.g., the on-time duration T₁ is the on-time durationdefined by when the switch-mode converter would have been simplyoperating in DCM). When the timer reaches the end of the on-timeduration T₁, the off-time duration T₂ (e.g., the off-time duration T₂ isthe off-time duration defined by when the switch-mode converter wouldhave been simply operating in DCM) is calculated or determined. The FSMalgorithm then moves to state S1 in which switch 108 turns off, and thetimer is reset. FSM algorithm stays at state S1 until the timer tracksand waits an off-time duration T₂/2.

When the timer reaches the end of the off-time duration T₂/2, FSMalgorithm then moves to state S2 in which the switch 108 is turned backon. Timer is again reset. FSM algorithm stays at state S2 until thetimer tracks, and waits an on-time duration T₁/2. When the timer reachesthe end of the on-time duration T₁/2, FSM algorithm then moves to stateS3 in which the switch 108 is turned back off. Timer is then reset. FSMalgorithm stays at state S3 until the timer tracks and waits theoff-time duration T₂. FSM algorithm then returns to state S0 and repeatsthe process therefrom.

FIG. 5A depicts a plot 500 which is identical to the plot 300 shown inFIG. 3A. Plot 500 in FIG. 5A is used for comparing, exemplary currentwaveforms that are shown for operating the switch-mode converter in DCMwith exemplary current waveforms in plot 502 in FIG. 5B for aswitch-mode converter operating in the hybrid DCM/CCM mode.

Referring now to the specific example in plot 502 of FIG. 5B, the chargearea Q1 defined by a first set of bolded boundaries represents thecharge defined in a first portion of the current waveform for inductorcurrent i_(L) when the switch-mode converter is operating in the hybridDCM/CCM mode. The area Q1 in FIG. 5B is identical to the area Q1 definedby the bolded boundaries in FIG. 5A since area Q1 represents the chargedefined for a single switching period of the current waveform forinductor current i_(L) when the switch-mode converter is simplyoperating in DCM. Plot 502 further shows an additional charge area-Q2defined by a second set of bold boundaries. Area Q2 defines new/addedcharge for a second portion of the current waveform for inductor currenti_(L) when the switch-mode converter is operating in the hybrid DCM/CCMmode. Plot 502 further shows a further additional charge area Q3 definedby a third set of bold boundaries. Area Q3 defines new/added charge fora third portion of the current waveform for inductor current i_(L) whenthe switch-mode converter is operating in the hybrid DCM/CCM mode. Sincethree pulses P1, P2, and P3 (e.g., total N number of pulses=3 pulses inthis case wherein N>1) are defined in the switching period, theswitch-mode converter in this case is considered to be operating in thehybrid DCM/CCM triple-pulse mode. In this exemplary case, the switchingpulse P2 is considered to be a subsequent pulse that is after theinitial switching pulse P1 and before the last switching pulse P3.

In this example of FIG. 5B, n is equal to 2 since pulses P2 and P3 areadded, and r is set equal to 0.5. The total charge being transferred forthe switching period, is then calculated as:

Total Charge Q=Q1*(1+2(1−(1−0.5)²))=2.5*Q1  Equation H

The total time duration TT′ for the switching period is defined as:

$\begin{matrix}\begin{matrix}{{TT}^{\prime} = {\left( {T_{1} + T_{2}} \right)*\left( {1 + {2*0.5}} \right)}} \\{= {{2*\left( {T_{1} + T_{2}} \right)} =}} \\{= {2*{TT}}} \\{= {2*\left( {4\mspace{14mu} {{microsec}.{+ 2}}\mspace{14mu} {{microsec}.}} \right)}} \\{= {12\mspace{14mu} {{microseconds}.}}}\end{matrix} & {{Equation}\mspace{14mu} I}\end{matrix}$

In other words, the total time duration TT′ for the switching perioddefined when the switch-mode converter is operating in the hybridDCM/CCM mode (e.g., FIG. 5B) is 2 times longer than the switching perioddefined when the switch-mode converter is simply operating in DCM (e.g.,FIG. 5A). FIG. 5R also shows that the total time duration TT′ is the sumof on-time duration T₁+off-time duration T₂/2+on-time durationT₁/2+off-time duration T₂/2+on-time duration T₁/2+off-time duration T₂+.This break down of the total time duration TT will be used for thetiming in controlling activation and deactivation of the switch (e.g.,switch 108).

The current comparison ratio between the hybrid DCM/CCM mode and the DCMmode is then calculated as follows:

$\begin{matrix}\begin{matrix}{\frac{i_{average}}{i_{target}} = \frac{\left( {1 + {2\left( {1 - \left( {1 - 0.5} \right)^{2}} \right)}} \right)}{\left( {1 + {2*0.5}} \right)}} \\{= \frac{2.5}{2}} \\{= 1.25}\end{matrix} & {{Equation}\mspace{14mu} J}\end{matrix}$

That is, the average current provided when the switch-mode converter isoperating in the hybrid DCM/CCM triple-pulse mode is 1.25 times thatwhen the switch-mode converter is simply operating in DCM. Thiscomparison is shown in FIG. 5B where the i_(average) line is at 1.25 Ampwhile the i_(target) line is at 1 Amp.

With reference now to FIG. 6, a state diagram 600 is shown for the FSM117 in FIGS. 1A and 1B. State diagram 600 shows how the FSM algorithmimplements the preferred switch control algorithm as characterized bythe exemplary current waveforms of FIG. 5B for operating the switch-modeconverter in the hybrid DCM/CCM triple-pulse mode. The timer that is inFSM 117 is also used to implement and execute the timing for the FSMalgorithm (e.g., switch control algorithm).

State diagram 600 shows that for this preferred control techniqueembodiment, FSM algorithm moves to a state. S0 in which the timer isreset. At state S0, switch 108 is on, and the timer waits for an on-timeduration T₁ (e.g., the on-time duration T₁ is the on-time durationdefined by when the switch-mode converter would have been simplyoperating in DCM). When the timer reaches the end of the on-timeduration T₁, the off-time duration T₂ (e.g., the off-time duration T₂ isthe off-time duration defined by when the switch-mode converter wouldhave been simply operating in DCM) is calculated or determined. The FSMalgorithm then moves to state S1 in which switch 108 turns off, and thetimer is reset. FSM algorithm stays at state S1 until the timer tracksand waits an off-time-duration T₂/2.

When the timer reaches the end of the off-time duration T₂/2, FSMalgorithm then moves to state S2 in which the switch 108 is turned backon. Timer is again reset. FSM algorithm stays at state S2 until thetimer tracks and waits an on-time duration T₁/2. When the timer reachesthe end of the on-time duration T₁/2, FSM algorithm then moves to stateS3 in which the switch 108 is turned back off. Timer is then reset. FSMalgorithm stays at state S3 until the timer tracks and waits an off-timeduration T₂/2. When the timer reaches the end of the off-time durationT₂/2, FSM algorithm then moves to state S4 in which the switch 108 isturned hack on. Timer is again reset. FSM algorithm stays at state S4until the timer tracks and waits an on-time duration T₁/2. When thetimer reaches the end of the on-time duration T₁/2, FSM algorithm thenmoves to state S5 in which the switch 108 is turned off Timer is againreset. FSM algorithm stays at state S5 until the timer tracks and waitsan off-time duration T₂. FSM algorithm stays at state S5 until the timertracks and waits the off-time duration. T₂. FSM algorithm then returnsto state S0 and repeats the process therefrom.

With reference now to FIG. 7, an exemplary power factor corrector 700 isshown. Power factor corrector 700 comprises full-wave diode bridgerectifier 103; capacitor 115; switch-mode converter 102, which is aswitch-mode boost converter/stage; and switch-mode converter controller114 which operates as a power factor correction (PFC) controller. Theseelements and components are coupled in the manner shown in FIG. 7. Theswitch-mode controller 114 (e.g., PFC controller) uses a finite statemachine 117 that has a timer. Switch-mode converter 102 further includesinductor 110, diode 111, switch 108, and capacitor 106. A line (mains)voltage source 101 can couple to the input of power factor corrector700, and a load 112 can couple to the output of power factor corrector700.

Switching of switch 108 may be calculated and performed so that theaverage current of boost inductor current i_(L), being the inputcurrent, varies proportionately with the rectified line input voltageV_(x)(t) where the proportionality ratio is selected such that thecapacitor link voltage/output voltage V_(c)(t) is regulated. Switch-modeconversion controller 114 (PFC controller) and its operations andfunctions can be implemented on a single integrated circuit. A voltagedivider comprising resistors R1 and R2 is coupled to the input of theswitch-mode converter controller 114 where the input voltage V_(x)(t) isfed in, and another voltage divider comprising resistors R3 and R4 iscoupled to the input of the switch-mode converter controller 114 wherethe link output voltage V_(c)(t) is fed in. The values for resistors R1,R2, R3, and R4 are selected so that the voltage dividers scale down theline input voltage V_(x)(t) and link output voltage V_(c)(t) to scaledline input voltage V_(xIC)(t) and scaled link output voltage V_(cIC)(t)that can be used for an integrated circuit.

In a power factor corrector, there are times in which extra current isdesired for a short period of time. Such exemplary times include but arenot limited to the time at the peak of the input sine-wave at low-lineoperation, during recovery from temporary input sag or brown-out, duringstart-up, and during load transients. The switch-mode convertercontroller 114 (e.g., PFC controller) that implements and executes theFSM algorithm (e.g., switch control algorithm) for controlling switch108 to operate the switch-mode boost converter/stage 102 in the hybridDCM/CCM mode can provide the advantages of providing such additionalcurrent during these times without adding additional components orcomplexity to the overall power factor corrector. Such advantages canfurther provide cost-savings and improve efficiency for the overallpower factor corrector.

Furthermore, an error may exist between the actually observed off-timeduration T₂ (e.g., observed as the actual off-time or flyback time ofswitch 108) and the above mathematically calculated off-time durationT₂. Such an error e is calculated as follows:

e=Calculated T ₂−Observed T ₂  Equation K

The error e can be compensated by dividing it among and during theoff-times provided by the additional pulse(s) such that the currentwaveform for the inductor current I_(L) (e.g., in FIGS. 3B and 5B) doesnot ramp or decay. For example, if the off-time T₂=Calculated T₂/2, thenthe updated off-time T2 maybe Updated Off-Time T₂=Calculated T₂/2−e/4.The inductor current i_(L) can be accurately controlled after making afew iterations of error compensation. Such compensation for error eallows for a larger n number of pulses to be, added to the switchingperiod and in effect allow the average current i_(average) be madehigher. Such error compensation also allows the actual switch-modeconversion system to be calibrated against the mathematically modeledswitch-mode conversion system.

An additional benefit of operating a switch-mode current in the hybridDCM/CCM mode exists, even when operating it in DCM would be adequate forthe required current. For example, when operating the switch-modeconverter in the hybrid DCM/CCM mode, the current waveform for theinductor current i_(L) is less repetitive, which causes less radiofrequency interference (RFI) than when simply operating the switch-modeconverter in DCM.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended, claims.

1. A switching converter controller for controlling a switch-modeconverter which has a switch and an inductor coupled to the switchwherein the switch-mode converter receives an input voltage and providesan output voltage, comprising: a finite state machine configured tooperate the switch-mode converter in a hybrid discontinuous conductionmode (DCM)/continuous conduction mode (CCM) mode; and wherein the finitestate machine defines a switching period for a control signal forcontrolling the switch based on an on-time duration of the switch and anoff-time duration of the switch and wherein an average inductor currentis calculated for the switching period from the on-time-duration of theswitch and the off-time duration of the switch.
 2. The switchingconverter controller of claim 1 wherein the finite state machine definesthe switching period for the control signal for controlling the switchalso based on an N number of switching pulses defined within theswitching period wherein N is an integer greater than one and whereinthe average inductor current through the inductor is zero before aninitial switching pulse of the N number of switching pulses, is zeroafter a last switching pulse of the N number of switching pulses, and isnon-zero for all other times within the switching period.
 3. Theswitching converter controller of claim 2 wherein the N number ofswitching pulses is two switching pulses and the hybrid DCM/CCM mode isa hybrid DCM/CCM double-pulse mode.
 4. The switching convertercontroller of claim 2 wherein the N number of switching pulses is threeswitching pulses and the hybrid DCM/CCM mode is a hybrid DCM/CCMtriple-pulse mode.
 5. The switching converter controller of claim 2wherein for a subsequent switching pulse after the initial switchingpulse and before the last switching pulse, the switch is turned on for afraction of the on-time duration and the switch is turned off for thefraction of the off-time duration, wherein the fraction is greater thanzero and less than one and is defined by a ratio of a width of thesubsequent switching pulse to a width of the initial switching pulse. 6.The switching converter controller of claim 5 wherein the fraction isselected as an optimal value in a range between 0.25 and 0.50.
 7. Theswitching converter controller of claim 1 wherein the switchingconverter controller is a power factor correction (PFC) controller forcontrolling the switch-mode converter that is a switch-mode boostconverter.
 8. A method for controlling a switch-mode converter which hasa switch and an inductor coupled to the switch wherein the switch-modeconverter receives an input voltage and provides an output voltage,comprising: configuring to operate the switch-mode converter in a hybriddiscontinuous conduction mode (DCM)/continuous conduction mode (CCM)mode; defining a switching period for a control signal for controllingthe switch based on an on-time duration of the switch and an off-timeduration of the switch; and calculating an average inductor current forthe switching period from the on-time duration of the switch and theoff-time duration of the switch.
 9. The method of claim 8 furthercomprising: defining a switching period for the control signal forcontrolling the switch also based on an N number of switching pulsesdefined within the switching period wherein N is an integer greater thanone and wherein the average inductor current through the inductor iszero before an initial switching pulse of the N number of switchingpulses, is zero after a last switching pulse of the N number ofswitching pulses, and is non-zero for all other times within theswitching'period.
 10. The method of claim 9 wherein the N number ofswitching pulses is two switching pulses and further comprising:configuring to operate the switch-mode converter in a hybrid DCM/CCMdouble-pulse mode.
 11. The method of claim 9 wherein the N number ofswitching pulses is three switching pulses and further comprising:configuring to operate the switch mode converter in a hybrid DCM/CCMtriple-pulse mode.
 12. The method of claim 9 further comprising:defining a fraction, that is greater than zero and less than one, basedon a ratio of a width of a subsequent switching pulse after the initialswitching pulse and before the last switching pulse to a width of theinitial switching pulse; and for the subsequent switching pulse, turningon the switch for a fraction of the on-time duration and turning off theswitch for the fraction of the off-time duration.
 13. The method ofclaim 12 wherein defining the fraction further comprises: selecting anoptimal value for the fraction in a range between 025 and 0.50.
 14. Themethod of claim 8 further comprising: controlling the switch-modeconverter that is a switch-mode boost converter which is used in a powerfactor corrector.
 15. An integrated circuit which incorporates aswitch-mode converter controller for controlling a switch-mode converterwhich has a switch and an inductor coupled to the switch wherein theswitch-mode converter receives an input voltage and provides an outputvoltage, and wherein the switch-mode converter controller includes afinite state machine, the integrated circuit configured to: operate theswitch-mode converter in a hybrid discontinuous conduction mode(DCM)/continuous conduction mode (CCM) mode; define a switching periodfor a control signal for controlling the switch based on an on-timeduration of the twitch and an off-time duration of the switch; andcalculating an average inductor current for the switching period fromthe on-time duration of the switch and the off-time duration of theswitch.
 16. The integrated circuit of claim 15 further configured to:define the switching period for the control signal for controlling theswitch also based on an N number of switching pulses defined within theswitching period wherein N is an integer greater than one and whereinthe average inductor current through the inductor is zero before aninitial switching pulse of the N number of switching pulses, is zeroafter a last switching pulse of the N number of switching pulses, and isnon-zero for all other times within the switching period.
 17. Theintegrated circuit of claim 16 further configured to: set the N numberof switching pulses to two switching pulses; and operate the switch-modeconverter in a hybrid DCM/CCM double-pulse mode.
 18. The integratedcircuit of claim 16 further configured to: set the N number of switchingpulses to three switching pulses; and operate the switch-mode converterin a hybrid DCM/CCM triple-pulse mode.
 19. The integrated circuit ofclaim 16 further configured to: define a fraction, that is greater thanzero and less than one, based on a ratio of a width of a subsequentswitching pulse after the initial switching pulse and before the lastswitching pulse to a width of the initial switching pulse; and for thesubsequent switching pulse, turn on the switch for a fraction of theon-time duration and turn off the switch for the fraction of theoff-time duration.
 20. The integrated circuit of claim 19 furtherconfigured to: select the fraction as an optimal value in a rangebetween 0.25 and 0.50.
 21. The integrated circuit of claim 15 furtherconfigured to: control the switch-mode converter that is a switch-modeboost converter which is used in a power factor corrector.
 22. A powerfactor corrector (PFC), comprising: a switch-mode boost stage having aswitch and an inductor coupled to the switch wherein the switch-modeboost stage receives a rectified line input voltage and provides a linkoutput voltage; a target current generator for receiving the link outputvoltage and for generating a target current proportionate to therectified line input voltage; and a finite state machine configured tooperate the switch-mode boost stage in a hybrid discontinuous conductionmode (DCM)/continuous conduction mode (CCM) mode wherein the finitestate machine defines a switching period for a control signal forcontrolling the switch based on an on-time duration of the switch and anoff-time duration of the switch and wherein an average inductor currentis calculated for the switching period from the on-time duration of theswitch and the off-time duration of the switch.
 23. The PFC of claim 22wherein the finite state machine defines the switching period for thecontrol signal for controlling the switch also based on an N number ofswitching pulses defined within the switching period wherein N is aninteger greater than one and wherein the average inductor currentthrough the inductor is zero before an initial switching pulse of the Nnumber of switching pulses, is zero after a last switching pulse of theN number of switching pulses, and is non-zero for all other times withinthe switching period.
 24. The PFC of claim 23 wherein the N number ofswitching pulses is two switching pulses and the hybrid DCM/CCM mode isa hybrid DCM/CCM double-pulse mode.
 25. The PFC of claim 23 wherein theN number of switching pulses is three switching pulses and the hybridDCM/CCM mode is a hybrid DCM/CCM triple-pulse mode.
 26. The PFC of claim23 wherein for a subsequent switching pulse after the initial switchingpulse and before the last switching pulse, the switch is turned on for afraction of the on-time duration and the switch is turned off for thefraction of the off-time duration, wherein the fraction is greater thanzero and less than one and is defined by a ratio of a width of thesubsequent switching pulse to a width of the initial switching pulse.27. The PFC of claim 26 wherein the fraction is selected as an optimalvalue in a range between 0.25 and 0.50.